The present invention relates generally to printing apparatus and more particularly to a device which both improves the quality of printed images and lowers printing costs.
The printing of images on articles, and particularly clothing (such as T-shirts and the like), is commonly accomplished by screen printing machines. Generally, these machines are provided with a print squeegee which is stroked across the surface of the screen so as to force printing ink through the screen, thereby effecting printing. Screen printing apparatus of this general configuration are disclosed, for example, in U.S. Pat. Nos. 3,795,189 and 4,939,991, the disclosures of which are hereby incorporated by reference.
In operation, the clothing or other material to receive the printed image are placed on pallets so that the surface to be printed upon is exposed. The pallets are then indexed to each in a series of printing stations. At each station, a printing head lowers the printing screen to a position slightly above the print surface. Upon stroking a flood bar and squeegee assembly back and forth across the screen, an image is printed on the article surface. During a first step of printing, the flood bar is lowered to a position in contact with the screen and passed over the screen, spreading printing ink over the screen surface. Next, the flood bar is raised and the squeegee is lowered into contact with the screen. The squeegee is passed back over the screen, momentarily forcing the screen into contact with the printing surface while forcing ink through the screen to effect printing.
As the flood bar is stroked across the screen, a wave of ink is formed which the flood bar pushes over the screen surface. During this operation, the ink has a tendency to flow toward the edges of the flood bar. After a few printing strokes, most of the ink accumulates on the sides of the screen, outside the path of the flood bar and squeegee. To reuse the accumulated ink, it is manually scraped toward the center of the screen on a regular basis.
Although conventional flood bars have been found effective in spreading ink, airborne lint and other debris constantly mix with the accumulated ink, eventually clogging the screen mesh and causing misprints. It was then necessary to halt printing operations to clean the screen. While clogging has been decreased (and production maintained) by periodically adding new ink to the screen surface, large amounts of ink accumulated. This was costly not only in wasting ink, but also delaying clean up.
To help contain the ink, the ends of the flood bars have been bent inwardly, e.g., at a 45.degree. angle. Other flood bars have been formed in a concave shape. Either way, conventional flood bars have met limited success in controlling the flow of ink. Moreover, the concave designs have been found to substantially increase the spacing between the squeegee and the flood bar which is undesirable.